This invention relates to a thermosetting resinous composition which cures into a rigid state upon heating through the ring-opening reaction of 2-oxazolidinone ring with amine into a urea linkage. It also relates to a novel compound or resin having a plurality of 2-oxazolidinone rings in the molecule which constitutes one of components of said thermosetting resinous composition.
In the coating industry, there is a long standing demand for a thermosetting resinous composition or system which is stable at room temperature but may be cured to a rigid film upon heating at an elevated temperature without emitting any by-product. Heretofore, thermosetting compositions containing etherified melamine resins or blocked polyisocyanates have been widely used in the coating industry. Compositions containing etherified melamine resins, however, emit an alcohol which has been used to etherify the melamine resin, while compositions containing blocked polyisocyanates emit a blocking agent such as alcohols, phenols, lactams or oximes. The emission of these by-products are undesirable not only for environmental reasons but also for technical reasons. Namely, it increase the amount of internal stress developed in the cured film resulting in poor appearance and other properties.
Epoxy resins and polyurethane or polyurea resins may be used for coating purposes. However, they are generally curable even at room temperature and thus must be formulated in a two components paint composition. Moreover, they are not usable in water-borne paints as a film-forming component.
It is known from literatures e.g. Bull. Soc. Chem. France, 1069 (1957); and ibid. 1841 (1959); that 2-oxazolidinone compounds otherwise known as cyclic urethanes may be ring-opened with an amine to produce corresponding urea derivatives. U.S. Pat. No. 3,519,608 and Bull. Chem. Soc. Jpn., 61 (10), 3559(1988) disclose a linear polymer having a plurality of 2-oxazolidinone ring-containing pendant groups. However, these literatures neither disclose nor suggest to utilize the above ring-opening reaction of 2-oxazolidinone ring in the production of polyurea polymers in which a number of urea linkages are recurring.
Accordingly, it is a major object of this invention to provide a novel thermosetting resinous composition containing 2-oxazolidinone and amine components capable of curing into a rigid state upon heating at an elevated temperature to produce a polyurea polymer without emitting any by-product.
It is another object of this invention to provide a novel 2-oxazolidinone derivative usable in the above resinous composition as the 2-oxazolidinone component thereof as well as an improved method for preparing said 2-oxazolidinone derivative.
Other objects and advantages of this invention will become apparent to those skilled in the art as the description proceeds.